The present invention relates to communications devices or the like and more particularly to a method and device for determining a location of a communications device or similar device capable of transmitting or receiving a radio frequency or electromagnetic signal.
Under various circumstances, determining a location of a communications device or a communications device operating in a transmit mode (transmitter) or a receive mode (receiver) may be important. For example in military, law enforcement or other applications being able to determine a geographic location of a radio transmitter may be very beneficial, particularly being able to determine the location when the transmitter and receiver are not in a line of sight transmission path or non-line of sight (NLOS) path with one another. NLOS paths may be sufficiently strong that phase coherent techniques fail, or insufficient space exists for directional antennas on receivers. Such scenarios may occur in close quarters operations or when the transceiver and receiver may be in the same building.
Determining a location of a transmitter may be helpful in radio navigation. One technique of determining a geographic location of a transmitter is trilateration. Trilateration requires a minimum of three range measurements to determine a receiver location. Existing solutions that require line of sight (LOS) paths for trilateration fail in cases where less than three transmitters are available or when less than three detectable LOS signals are available due to path attenuation. Current solutions when three available transmitter or LOS signals are not available may include increasing the number of transmitters to increase the probability that at least three may be available, change the radio parameters of the link, such as frequency, antenna diversity, polarization diversity or other parameters, rely on other means of navigation, such as inertial devices or the like, to temporarily replace the trilateration navigation until more transmitters or acceptable transmission paths become available.
Increasing the number of available transmitters increases operating costs and may decrease survivability of the system for operations such as military operations or similar operations. Changing radio parameters of the link increases complexity of transmitters and receivers and requires communications between the transmitters and the receivers to change the radio parameters. The accuracy of inertial devices tends to decrease over time.